With MVVM, does each UI window have its own ViewModel?

Question

When I\'m designing multiple views under the MVVM pattern, does each view get its own ViewModel or do they all share the same one? I understand that this is ultimately a flexib

Answer 1

To me thats a subjective statement- text book, I would say definately a 1-1 pairing - and there is certainly nothing wrong w/ being proactive and setting the paradigm by having a 1-1. However, if you have multiple views each representing a slice of the same data you dont necessarily have to have 1 per- you could reuse the same one across multiple views until you had a deviation. The purpose of the view model being a bridge between the ui and the business layer...if the business functions are the same you are either going to have a common view model interface or base and cast down or you are going to be replicating the same logic multiple times. If the view is the only thing that changes I see no issue in reusing the same view model until there is deviation.

In wpf, you should be binding to values on the model so unless your view model has a reference to your concrete view that shouldnt be an issue. Even it does, you could abstract out to a view contract (interface) and change the property to be that type instead.